Guide
What is nitrous oxide? The chemical name the formula N₂O, why it is called laughing gas, and how it is used and controlled
Nitrous oxide is N₂O, chemical name dinitrogen monoxide, a colourless, non-flammable gas of molar mass 44.013 g/mol. Joseph Priestley first made it in 1772; Humphry Davy's 1799 inhalation trials earned it the name laughing gas. Today it is an anaesthetic, a food propellant and an analytical oxidant.
- Names and formula
- Nitrous oxide; dinitrogen monoxide
- First prepared
- 1772
- Laughing gas
- Humphry Davy first breathed it in April 1799 and published a study of nearly 600 pages in 1800 that suggested its use against surgical pain
- First anaesthetic use
- December 1844
- Physical state
- Liquefied in the cylinder at 50.5 bar at 20 °C; critical temperature 36.4 °C; boils at −88.5 °C
Nitrous oxide is the gas with the formula N₂O: two atoms of nitrogen and one of oxygen, joined in a line. Its systematic name is dinitrogen monoxide, its everyday name laughing gas, and in a cylinder it is a liquefied gas at about 50 bar. It is colourless, does not burn, but supports combustion vigorously. It has been made for more than 250 years, was one of the first anaesthetics, used in dentistry from 1844, and is still used in hospitals, kitchens, laboratories and race cars. This page explains the names, the formula, the history and the uses, and states the safety and legal position plainly.
Names, formula and identity
| Item | Value | Source |
|---|---|---|
| Common name | Nitrous oxide | — |
| Systematic names | Dinitrogen monoxide; dinitrogen oxide | IUPAC naming practice |
| Popular names | Laughing gas; "nitrous" or NOS in motorsport | — |
| Formula | N₂O, linear N–N–O | NIST Chemistry WebBook |
| Molar mass | 44.013 g/mol | NIST Chemistry WebBook |
| CAS number | 10024-97-2 | NIST Chemistry WebBook |
| Food additive number | E942 | Codex numbering system |
| Transport identity | UN 1070, Class 2.2 with subsidiary risk 5.1 (oxidiser) | IS 4379:2021 Table 1 (UN number); UN Model Regulations (class) |
| Boiling point | −88.5 °C at 1 atm | NIST Chemistry WebBook |
| Critical temperature | 36.4 °C | NIST Chemistry WebBook |
| Medical cylinder colour | French blue (166) | IS 3933:2021 Table 1 |
The name confuses people because there are several nitrogen oxides. Nitrous oxide, N₂O, is the stable, low-toxicity one used in medicine. Nitric oxide, NO, and nitrogen dioxide, NO₂, grouped as NOx, are toxic gases from vehicle exhausts and furnaces; nitrogen dioxide is the brown one. Medical specifications limit NO and NO₂ in medical nitrous oxide for exactly that reason. The physical data for N₂O, including its vapour pressure and densities, are on the nitrous oxide technical data page.
A short history
| Year | Event | Source |
|---|---|---|
| 1772 | Joseph Priestley prepares the gas from nitric acid and iron filings and calls it dephlogisticated nitrous air | Chemistry World |
| 1798 | Humphry Davy becomes superintendent of Thomas Beddoes's Medical Pneumatic Institution, founded to test new gases as medicines | Science History Institute |
| April 1799 | Davy first inhales nitrous oxide and records its effects on himself | Chemistry World |
| 1800 | Davy publishes his book of nearly 600 pages, Researches, chemical and philosophical, chiefly concerning nitrous oxide, noting that the gas appears capable of destroying physical pain | Chemistry World |
| 1802 | A James Gillray cartoon, Scientific Researches, satirises a Royal Institution lecture on gases, with Davy holding the bellows | Science Museum Group collection |
| December 1844 | The dentist Horace Wells has a tooth extracted under nitrous oxide and begins using it on patients; his public demonstration in Boston in January 1845 is judged a failure | Chemistry World |
| 1863–1866 | Gardner Quincy Colton re-establishes it in dentistry, treating more than 25,000 patients | Chemistry World |
The history has an odd gap. Davy suggested in 1800 that nitrous oxide might be used in surgery, yet it was nearly half a century before anyone tried, and ether and chloroform, introduced in 1846 and 1847, overtook it for major operations. Nitrous oxide survived because it acts quickly and wears off quickly, which suits dentistry, childbirth and emergency pain relief.
Why it is called laughing gas
At low concentrations nitrous oxide produces light-headedness, euphoria and, in some people, laughter. Davy and his circle at Bristol described exactly this, and public demonstrations after 1800 turned it into an entertainment. The nickname stuck. The effects are real but they are pharmacological: the gas acts on the nervous system, and a person breathing it is also breathing less oxygen. In medicine it is therefore given mixed with oxygen, commonly as a 50 % mixture, so the patient is never short of oxygen.
How nitrous oxide is made and supplied
Industrial nitrous oxide is made by the controlled thermal decomposition of ammonium nitrate, followed by purification, compression and liquefaction. It is supplied as a liquefied gas in cylinders, where the pressure depends only on temperature: NIST gives 50.5 bar at 20 °C. The contents are measured by weight, not by pressure, for the reason explained under permanent vs liquefied gases.
Uses
| Use | How the gas is used | Grade |
|---|---|---|
| Anaesthesia and analgesia | Inhaled, usually mixed with oxygen, for pain relief in labour, dentistry and emergency care, and as a carrier for other anaesthetic agents | Medical, to the Indian Pharmacopoeia |
| Food | Propellant and whipping agent for cream, where it dissolves in the fat and expands on release | Food grade, additive E942 |
| Atomic absorption spectrometry | Oxidant for the nitrous oxide–acetylene flame, about 2,800 °C, used for elements that form refractory oxides, such as aluminium and silicon | Analytical |
| Motorsport | Injected into an engine intake; it decomposes in the combustion heat and releases oxygen | Industrial |
| Industry and research | Oxidant and process gas in electronics and laboratory work | Industrial or high purity |
The flame use matters to KIGL's acetylene customers: the nitrous oxide–acetylene flame is one of the main laboratory uses of high-purity acetylene. More detail on each use is on uses of nitrous oxide.
Rules that matter
Nitrous oxide is not flammable, but it is not harmless. The facts, stated neutrally:
Safety and misuse
- It is an oxidiser It supports combustion and breaks down to nitrogen and oxygen with a release of heat, so oil and grease must be kept from its valves and regulators, as with oxygen.
- It is an asphyxiant in high concentration Breathing it undiluted displaces oxygen from the lungs, and deaths from hypoxia have occurred in people inhaling it outside medical care.
- Expanding gas is very cold Gas released from a cylinder or charger cools sharply and can freeze the lips, mouth and airway.
- Repeated heavy use harms the nerves The UK Advisory Council on the Misuse of Drugs, in its 6 March 2023 harms assessment, reported increasing neurological harm associated with exceptionally heavy and persistent use. Clinical reports attribute this to inactivation of vitamin B12.
- Staff exposure has recommended limits The ACGIH limit is 50 ppm as an 8-hour time-weighted average, and NIOSH recommends 25 ppm during anaesthetic administration, which is why operating theatres scavenge waste gas.
The full set of hazards, with first aid and fire-fighting, is on nitrous oxide safety data explained and the safety data sheet.
Legal supply in India
Medical nitrous oxide is a drug. It is manufactured and tested to the Indian Pharmacopoeia monograph under a manufacturing licence issued under the Drugs and Cosmetics Act, 1940, released batch by batch with a certificate of analysis, and filled into cylinders painted French blue (166) on body and shoulder under IS 3933:2021. Storage and handling of the cylinders also fall under the Gas Cylinders Rules, 2016, administered by PESO. Industrial and food grades are sold to businesses with a documented use. A responsible supplier asks what the gas is for and refuses supply for inhalation outside medical care. Supply enquiries go through the nitrous oxide gas page.
Rules that matter
What this means for you
- Use the name nitrous oxide, or N₂O, on orders and documents; laughing gas is a nickname, and nitric oxide is a different gas.
- Buy medical nitrous oxide only as a medical product, in a French blue cylinder with a batch certificate.
- Treat N₂O fittings as oxidiser fittings: oil-free and opened slowly.
- Weigh cylinders to know their contents.
- Never inhale it outside medical supervision, and do not supply it to anyone who intends to.
What is nitrous oxide? — frequently asked questions
What is the chemical name of N2O?
Dinitrogen monoxide, also written dinitrogen oxide. The common name is nitrous oxide and the popular name laughing gas. The formula N₂O means two nitrogen atoms and one oxygen atom in a straight line, N–N–O. It should not be confused with nitric oxide (NO) or nitrogen dioxide (NO₂), which are toxic air pollutants with quite different properties.
What is the gas name of N2O?
Nitrous oxide. In medicine it is simply called nitrous oxide or N₂O; in food labelling it is additive E942; in motorsport it is called nitrous or NOS; and in everyday speech laughing gas. All refer to the same compound, CAS 10024-97-2, with a molar mass of 44.013 g/mol (NIST).
Why is nitrous oxide called laughing gas?
Because of the euphoria and laughter it produced in the inhalation experiments Humphry Davy ran at the Pneumatic Institution in Bristol from 1799, and in the public demonstrations that followed. James Gillray's 1802 cartoon of a Royal Institution lecture on gases helped make the joke famous. The euphoria is a drug effect of the gas on the brain, which is why it is used medically for pain relief.
Who discovered nitrous oxide?
Joseph Priestley, the English chemist, in 1772. He made it by reacting nitric acid with iron filings and called it dephlogisticated nitrous air. Its effects on people were explored later by Humphry Davy, from 1799, and its use as an anaesthetic began with the American dentist Horace Wells, who had one of his own teeth extracted under the gas in December 1844.
Is laughing gas the same as the nitrous used in cars?
Chemically, yes: both are N₂O. Motorsport systems inject it into the engine intake, where it decomposes in the heat of combustion and releases its oxygen, letting more fuel burn. The grades, cylinders and fittings differ from medical supply, and medical nitrous oxide is a drug that must not be diverted to other uses.
Is medical nitrous oxide classed as a drug in India?
Yes. Medical nitrous oxide is a drug under the Drugs and Cosmetics Act, 1940, made to the Indian Pharmacopoeia under a manufacturing licence and supplied to hospitals and licensed medical users. Industrial and food grades are supplied to businesses with a documented use. A responsible supplier asks what the gas is for; recreational supply is refused.
References
- Bureau of Indian Standards. (2021). Colour identification of medical gas cylinders (IS 3933:2021).
- Chemistry World (Royal Society of Chemistry) — the history of nitrous oxide, Priestley, Davy, Wells and Colton
- Linstrom, P. J., & Mallard, W. G. (Eds.). (n.d.). NIST Chemistry WebBook (NIST Standard Reference Database 69). National Institute of Standards and Technology. [Nitrous oxide] https://webbook.nist.gov/cgi/cbook.cgi?ID=C10024972
- Science History Institute — Humphry Davy historical profile
- Science Museum Group collection — James Gillray, Scientific Researches, New Discoveries in Pneumaticks (1802)
- UK Advisory Council on the Misuse of Drugs — Nitrous oxide updated harms assessment, 6 March 2023 https://www.gov.uk/government/publications/nitrous-oxide-updated-harms-assessment
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